I have a brass wire manufacturing plant. The wire is of CDA270 ( Cu-Zn, 63%-37% ) grade and is use to make machine screws (Philips head etc). When the screws are made from this wire, there is roughness found on the screw head. The head of the screw must be smooth. I suspect that the drawing and annealing process which is used to make wire is responsible for this.

The draw and annealing process which we follow is as below

1) First 10 mm Brass wire is drawn down to 8 mm wire.
2) This then undergoes annealing in Electric Pot Furnace.
3) Then we again draw it to reduce by 1.5 mm and again annealing is done. (The diameter of wire before the last annealing will be 10% more than what our finished product size has to be. And final draw will reduce the remaining 10% from the wire).

I am not sure if the above mentioned drawing and annealing process is responsible for the quality of final Brass wire.

Any advice to resolve this will be a great help to me. Please let me know if anyone has any suggestions. Also let me know if any other information is required to understand the problem.

While a pot furnace will give you a good thermal soak, I wonder just how much accurate control you have over the annealing process itself. Keep in mind that the prior thermal and mechanical history needs to be known as recrystallization and annealing occur much faster in a more heavily cold worked alloy. Excessive grain growth can result from too much time at temperature. Possibly there is no recirculating air in your pot furnace and thus thermal stratification can occur.

You can purchase the following books and specifications or perhaps there is a technical or a local engineering library with these already in it.

(1) ASTM B601 gives multiple sets of annealing tempers for copper & its alloys, some based upon prior mechanical processing, some based upon grain size.
For example:
- OS005 is annealed, with final average grain size of 0.005 mm.
- OS200 is annealed, with final average grain size of 0.200 mm.
- O81 is an 'Annealed to' temper - Hard material annealed down to 1/4 Hard.
(1a) ASTM B601-07 Standard Classification for Temper Designations for Copper and Copper Alloys—Wrought and Cast.
www.astm.org/cgi-bin/SoftCart.exe/DATABA...m?L+mystore+eulz4392

Book (c) may be the one most important for you. The non-member price is $US 251.00.

Finally, I reviewed EBNER Industrieofenbau Gesellschaft m.b.H., a well renowned manufacturer of copper and copper alloy batch annealers in Austria, (
www.ebnerhicon.at/
) and I saw no pot furnaces for copper alloys.

Perhaps, as you have already suspected, this is your basic problem. Some experimentation with a small but accurate annealer at some other location will provide you with the answers you are looking for.

Batch annealing in notoriously inaccurate, especially is the customer wants to achieve anything else but a fully annealed product.

Looking at your process description I see that you are doing a final draw with only 10% reduction, indicating that you need a ¾ or ½ hard wire.

Utilizing a Plasma Annealer will allow you to process your wire in-line and directly to the required temper. Such a system will not only permit you to accurately control the annealing process but will also reduce your production costs significantly. The up-front investment costs, however, and not indifferent.

Peter, as suggested by you I will first try to experimenting with reducing the annealing temperature and period of annealing. Also I had a look in to links you have provided and it is helpful. Probably I will be ordering one of them to understand the properties of Brass metal.

Also if there is any other book or link which is dedicated to experiments of drawing and annealing on Brass metal, please let me know.

Willy, I went to the website you provided. The size for which we need Annealers will have to be custom made by Plasmait. Will check with the Plasmait guys regarding the same.

It was fruitful for me to post my issue here. And I am very thankful to both of you.

Will do some reading and experimenting now. Will keep updating if I find any useful information or solution for my problem. Also if I have any further doubts or query will post again.

Hello Priyanshu,
If we talk about high quality with the annealing of brass wire, then we recommend the use of an induction annealer.
The advantages are those that no contact at the surface of the wire is necessary for feed in current and thus an optimum surface quality leaves the machine. Please visit the attached web page and contact us for any question.
www.buehler-co.de